WISArD experiment

The Weak Interaction Studies with 32Ar Decay (WISArD) experiment is a permanent experimental setup located in the ISOLDE facility, at CERN. The purpose of the experiment is to investigate the weak interaction by looking for beta-delayed protons emitted from a nucleus. In the absence of online isotope production during Long Shutdown 2, the experimental setup has also been used to measure the shape of the beta energy spectrum. A goal of the experiment is to search for physics beyond the Standard Model (SM) by expanding the existing limits on currents in the weak interaction.

The WISArD experimental setup reutilises the WITCH experiment's superconducting magnet and existing infrastructure.

Background

The Standard Model describes three of the four fundamental interactions and classifies all known elementary particles. Whilst being essentially confirmed by the discovery of the Higgs boson, there are still many unanswered questions, specifically regarding the weak interaction. The Standard Model proposes a specific Vector – Axial Vector (V – A) formalism for the weak interaction, however other contributions are not excluded by theory. Measurements of well-selected beta decays, such as pure Fermi (F) or pure Gamow-Teller (GT) decays, may provide experimental evidence for these other contributions, as beta decays cause minimal disturbances from effects relating to nuclear structure and the pure transitions are independent of underlying nuclear interactions.

By determining the momentum of the beta particle and the neutrino, a correlation coefficient that quantifies the extent of non-SM contributions can be determined. However, it is essentially impossible to observe and measure the neutrino in this kind of experiment.